California Air Resources Board

The Issue

One of the air pollutants of greatest concern for California and the nation has been particulate matter, especially PM2.5. PM2.5 is a complex pollutant composed of microscopic particles 2.5 micrometers or smaller that can be inhaled deep into the lungs. PM2.5 can be directly emitted from combustion or formed by chemical processes in the atmosphere. Long-term exposure to particulate matter, such as PM2.5, has consistently been linked to premature  death¹. The strongest association has been with deaths from cardiovascular causes. However, previous studies on the health effects of exposure to PM2.5 typically include individuals from across the U.S. who may be subject to conditions that are different from those found in California. Previous studies have also raised the issue of how inhaled PM2.5 affects the cardiovascular system. Scientists have recently started to study cardiovascular function, since alterations in these functions are hallmarks of cardiovascular disease.

Research Goals

In order to address this research gap, the studies discussed here examine the impact of air pollution on a population of men and women in California and on a separate population of elderly women educators (which may represent a more sensitive population). Understanding whether and how inhaled PM2.5 can alter cardiovascular cellular functions pose challenges that limit our ability to adequately assess the level of risk that exposure to PM2.5 poses to cardiovascular health. These studies, funded by the California Air Resources Board (CARB) and the South Coast Air Quality Management District, address how the cardiovascular health of Californians is affected by PM2.5 exposure statewide, and provide information on the mechanisms by which cardiovascular health is impacted.

Results

The statewide study of 76,000 men and women tracked from 1982 to 2000 found:

• Significant associations with PM2.5 exposure and elevated relative risks for death from cardiovascular disease, with the largest risk being observed for death due to heart attacks.
• Elevated risks for death due to heart attacks that were similar to the risks seen in national studies on the impact of PM2.5 exposure on premature death.

The study of 100,000 women in California found:

• Exposure to PM2.5 resulted in an elevated risk for death from heart attacks.
• Among post-menopausal women, exposure to PM2.5 resulted in an elevated incidence of stroke.

A third study was conducted on mice, and was designed to investigate mechanistic pathways that could explain how inhaled PM2.5 could contribute to heart attacks and strokes. A common cause of heart attacks and strokes is development of clots in the blood stream. One suggested explanation is that PM2.5 exposure activates platelets, the key cells involved in blood clotting, so that they form clots which then trigger heart attacks and strokes. The study examined the platelets of mice exposed to PM2.5 from the San Joaquin Valley Air Basin, in both urban and rural areas, and found platelet activation in both winter and summer, which could promote clotting and lead to stroke and heart attacks.

Conclusions and Impact

The results from the first two studies showed that PM2.5 exposure poses a health risk similar to that found in nationwide assessments. The third study used mice to investigate some of the potential mechanisms by which PM2.5 can damage the cardiovascular system and showed that PM2.5 can lead to heart-related illnesses. CARB estimates there were 7,300 to 11,000 annual premature cardiovascular or respiratory deaths associated with PM2.5 exposure in California from 2006 to 2008. PM2.5 in California mainly results from motor vehicle pollution, which is the focus of most of CARB’s control and incentive programs. These programs have led to a 42 percent reduction in annual-average PM2.5 levels from 2000 to 2011. Although air quality is improving in all communities throughout the state, these studies demonstrate that there is a need to continue to reduce exposure to PM2.5 in California.

Related Research

In addition to regulations to reduce mobile source pollution and other sources of PM2.5, CARB is also funding studies to reduce pollution exposures. These include development of guidance on the use and cost-effectiveness of in-duct and portable high-efficiency filtration for reducing exposure to air pollution from both indoor sources and outdoor sources that have infiltrated into the home. Another study is looking at the extent to which cabin filters in cars and school buses can reduce exposures to roadway pollution at a relatively low cost.

More Information

• 1U.S. Environmental Protection Agency. Integrated Science Assessment for Particulate Matter (Final Report). 2009.